Labor and Delivery Case File

Labor and Delivery Case File

Eugene C. Toy MD, Donald Briscoe, MD, FA  AFP, Bruce Britton, MD, Joel J. Heidelbaugh, MD, FA  AFP, FACG

Case 16

A 25-year-old G2P1 woman at 39-week estimated gestational age presents to the labor and delivery triage unit stating that her"water has broken." She reports having had a large gush of clear fluid followed by a constant leakage of fluid from her vagina. She subsequently started having uterine contractions approximately every 4 minutes. She has had an uncomplicated prenatal course with good prenatal care since 8-week gestation. Her prenatal records are available for review in the triage unit. Her first pregnancy resulted in the full-term delivery of a 7-lb 8-oz, healthy boy.

In the triage unit, she is placed on an external fetal monitor. Her blood pressure is 110/70 mm Hg, her pulse is 90 beats/min, and her temperature is 98.7°F (37.0°C). Her general examination is normal. Her abdomen is gravid, with a fundal height of 38 cm. The fetus has a cephalic presentation by Leopold maneuvers and an estimated fetal weight of 8 lb.

⯈ What signs and tests could confirm the presence of rupture of membranes?

⯈ On the fetal monitoring strip shown (Figure 16-1), what is the approximate baseline fetal heart rate? How often is she having uterine contractions?

⯈ Her prenatal records reveal that she had a positive group B Streptococcus (GBS) vaginal culture at 36-week gestation. What therapy should be instituted at this time?

Figure 16-1. External Fetal Monitoring Strip.

ANSWER TO CASE 16:

Labor and Delivery

Summary: A 25-year-old pregnant woman at term presents with the spontaneous rupture of membranes and subsequent uterine contractions, signaling the onset of labor.

• Signs that could confirm the rupture of membranes: Visualization of amniotic fluid leaking from the cervix; the presence of pooling of amniotic fluid in the posterior vaginal fornix; demonstration of a pH above 6.5 in fluid collected from the vagina using Nitrazine paper; or visualization of "ferning" on a sample of fluid on an air-dried microscope slide
• Baseline fetal heart rate: 140 beats/min
• Contraction interval: Approximately every 3 minutes
• Recommended antibiotic prophylaxis for GBS colonization during labor: Penicillin 5 million units IV loading dose followed by 2.5 million units IV every 4 hours; alternative treatments include IV ampicillin, cefazolin, clindamycin, and vancomycin

ANALYSIS

Objectives

1. Know the definition of labor, including the three stages of labor, understand the definitions and differences in the categories of fetal heart tracings, and know the normal progression of labor in nulliparous and multiparous women.
2. Understand the types of fetal monitoring that are routinely performed during labor and how monitoring correlates with the physiologic processes occurring during labor.
3. Be familiar with the abnormal progression of labor and some of the interventions that can be made to address these problems.

Considerations

This woman arrives at the labor and delivery triage unit in need of evaluation for the possibility that she is in labor and that she has ruptured her membranes (broken her bag of water). The accurate and appropriate diagnosis of labor is extremely important in obstetrical care. Incorrectly diagnosing a woman as being in labor may result in unnecessary interventions, whereas not diagnosing labor may result in complications or delivery occurring without access to appropriate personnel and facilities. Furthermore, the diagnosis of rupture of membranes is critical for several reasons. First, especially at term, the spontaneous rupture of membranes may signify the impending onset of labor. Second, if the presenting part is not well applied in the pelvis, prolapse of the umbilical cord with resultant compression of the cord and disruption of the oxygen supply to the fetus may occur. Finally, the prolonged rupture of membranes, especially after 24 hours or longer, may predispose to the development of infection.

The physician also must promptly make assessments of both maternal and fetal well-being. A careful history and physical examination should be performed. When available, prenatal records should be reviewed to evaluate for any problems during this, or previous, pregnancies and to confirm the gestational age of the pregnancy. In this case, the presence of GBS colonization requires the institution of appropriate antibiotic prophylaxis to reduce the risk of fetal infection with GBS, a common cause of neonatal morbidity and mortality. In GBS-colonized women, the recommended antibiotic prophylaxis is IV penicillin. When this is not available, ampicillin is often substituted. In penicillin-allergic women, cefazolin, clindamycin, or vancomycin can be used. Fetal well-being is most commonly monitored using external, electronic fetal-monitoring equipment, although other options are available. With this equipment, the baseline fetal heart rate, heart rate variability, accelerations and decelerations, along with the presence and frequency of uterine contractions, may be evaluated. Determination of the presentation of the fetus (cephalic, breech, or shoulder [ie, transverse lie]) is also critical, as this may play a significant role in the determination of route of delivery (vaginal or cesarean).

Approach To:

Labor and Delivery

DEFINITIONS

FETAL LIE: The relationship of the long axis of the fetus to the long axis of the mother; either longitudinal or transverse

FETAL PRESENTATION: The part of the fetus that is either foremost in the birth canal or in closest proximity to the birth canal

LABOR: Regular uterine contractions that lead to the effacement and dilation of the cervix

PREMATURE RUPTURE OF MEMBRANES: Rupture of the fetal membranes prior to the onset of labor

CLINICAL APPROACH

Labor usually begins spontaneously and occurs normally within 2 weeks of the estimated date of confinement (280 days after the first day of the last menstrual period). The onset of labor more than 3 weeks before the estimated date of confinement (EDC) is considered preterm labor. If labor has not started spontaneously by 2 weeks after the EDC, the pregnancy is considered postterm.

Stages of Labor

Labor is typically divided into three stages. The first stage of labor is from the onset of labor until the cervix is completely dilated. This stage can further be divided into a latent phase and an active phase. During the latent phase of labor, the contractions become stronger, longer lasting, and more coordinated. The active phase of labor, which usually starts at 3 to 4 cm of cervical dilation, is when the rate of cervical dilation is at its maximum. Contractions are usually strong and regular. In active labor in a woman without an epidural, the minimum expected rates of cervical dilation are 1.2 cm per hour for a nulliparous woman and 1.5 cm per hour for a parous woman. The second stage of labor is from complete cervical dilation (10 cm) through the delivery of the fetus. The combination of the force of the uterine contractions and the pushing efforts of the mother results in the delivery of the baby. A normal second stage lasts less than 2 hours in a nulliparous patient and less than 1 hour in a parous patient. The presence of epidural anesthesia can prolong these times by up to 1 hour. The third stage of labor begins after the delivery of the baby and ends with the delivery of the placenta and membranes. The third stage is typically short and is considered prolonged if it lasts longer than 30 minutes.

The Progress of Labor

The progress of labor usually depends on the "three Ps:" The Power is the strength of the uterine contractions during the active phase of labor and of the maternal pushing efforts during the second stage of labor. The power of the contractions can be assessed subjectively by an examiner palpating the uterus during a contraction or objectively by placing an intrauterine pressure catheter, which directly measures pressure within the uterine cavity. The Passenger is the fetus. Its size, lie, presentation, and position within the birth canal all play a role in the progression of labor and rate of fetal descent. Finally, the shape and size of the Pelvis can result in delay or failure of descent of the fetus because of the relative disproportion between the fetal and pelvic sizes.

The diagnosis of active labor is an indication for admission to the birthing unit for labor management and monitoring. The presence of ruptured membranes is also an indication for admission. The rupture of membranes can be confirmed by a careful vaginal examination performed with a sterile speculum and gloves. The visualization of fluid leaking from the cervical os, either spontaneously or with the patient performing a Valsalva maneuver, and the presence of amniotic fluid pooling in the posterior vaginal fornix are confirmatory. The detection of fluid in the vagina with a pH more than 6.5 is consistent with amniotic fluid, as normal vaginal secretions typically have a pH less than 5.5. Using a sterile applicator to sample vaginal fluid and applying it to Nitrazine paper can make this determination. The presence of semen, blood, or bacterial vaginosis can cause elevated pH in vaginal secretions and a false-positive Nitrazine test. The visualization of ferning of vaginal fluid under microscopic magnification of an air-dried sample also suggests the presence of amniotic fluid.

When the pregnant patient is admitted to the labor and delivery unit, fetal wellbeing is assessed by either continuous or intermittent fetal heart rate monitoring. Continuous external fetal heart rate monitoring is the more commonly used procedure in the United States. A Doppler ultrasound device is used to continuously trace the fetal heart rate. Continuous monitoring can also be accomplished using an internal device (fetal scalp electrode), by attaching an electrode to the fetal scalp that directly measures and amplifies fetal cardiac electrical activity. This procedure requires that the membranes are ruptured. With either of these two techniques, a continuous graphic recording of the fetal heart rate is recorded. Alternatively, intermittent auscultation using a stethoscope or handheld Doppler can be performed. The American College of Obstetricians and Gynecologists (ACOG) recommends that in intermittent auscultation of low-risk pregnancies, the fetal heart should be monitored after a contraction at least every 30 minutes during the first stage of labor and every 15 minutes in the second stage. In at-risk pregnancies, the monitoring frequency is increased to at least every 15 minutes during the first stage and to every 5 minutes in the second stage.

Important considerations in interpreting fetal heart rate data are the baseline heart rate, variability, and periodic heart rate changes. The baseline heart rate is the approximate average heart rate during a 10-minute tracing. A baseline heart rate of 110 to 160 beats/min is considered normal, less than 110 beats/min is considered to be bradycardia, and greater than 160 beats/min is considered to be tachycardia. Fetal bradycardia may occur with maternal hypothermia, certain medications given to the mother, congenital heart block, or may be a sign of significant fetal distress. Bradycardia may also be a normal variant. The most common cause of fetal tachycardia is maternal fever. Other common causes include medications and fetal arrhythmias.

Variability is regulated by the balance of sympathetic and parasympathetic control of the sinoatrial node. Short-term variability is the change in fetal heart rate from one beat to the next and can only be accurately determined when an internal scalp electrode is placed. Normal short-term variability is 6 to 25 beats/ min. Longterm variability is the waviness of the baseline heart rate over 1 minute, with normal oscillations occurring at a rate of 3 to 5 cycles per minute. As variability is largely a manifestation of the autonomic nervous system, anything that affects nervous system functioning can affect it. Common causes of decreased variability are fetal sleep cycles, central nervous system (CNS) depressant drugs (such as narcotic analgesics) given to the mother, congenital neurologic abnormalities, and prematurity. Fetal acidemia secondary to hypoxemia can impair CNS function and reduce variability. The presence of normal variability makes fetal acidemia unlikely.

Periodic heart rate changes are the accelerations and decelerations from the baseline

heart rate that occur, often related to uterine contractions. An acceleration is

an increase in the fetal heart rate of 15 beats/min or more for 15 seconds or longer

and is a reassuring finding. The presence of accelerations, whether occurring

spontaneously or in response to contractions, fetal movement, or stimulation of

the fetus (either scalp stimulation during a cervical examination or vibroacoustic

stimulation using an artificial larynx) virtually ensures that the fetal arterial pH is

greater than 7.2.

Decelerations are generally defined as early, late, or variable based on the timing of the deceleration in relation to a contraction. An early deceleration coincides with a contraction in onset of the fetal heart rate decline and return to the baseline. Early decelerations are thought to be a result of increased vagal tone caused by compression of the fetal head and are not associated with fetal hypoxia or acidemia. A late deceleration is a gradual reduction in the fetal heart rate that starts at or after the peak of a contraction and has a gradual return to the baseline. Late decelerations are a manifestation of uteroplacental insufficiency and can be caused by numerous circumstances. Common among these are maternal hypotension, as is often seen with epidural anesthesia and uterine hyperstimulation caused by oxytocin administration. Conditions that impair placental circulation, including maternal hypertension, diabetes, prolonged pregnancy, and placental abruption, often contribute to late decelerations. A variable deceleration is an abrupt decrease in fetal heart rate, usually followed by an abrupt return to baseline that occurs variably in its timing, relative to a contraction. Variable decelerations are the most common types of decelerations seen during fetal heart monitoring and are considered to be due to umbilical cord compression during contractions. Variable decelerations, particularly when there is also the presence of normal variability and accelerations, are usually not associated with fetal hypoxemia.

Current fetal monitoring equipment also allows for contraction monitoring along with the fetal heart rate assessment. An external tocodynamometer is most commonly used. It allows for evaluation of the presence and timing of contractions but does not measure the strength of the contractions. To assess the strength of contractions, an internal intrauterine pressure catheter (IUPC) can be placed. Like the fetal scalp electrode, this requires the presence of ruptured membranes. An IUPC can be useful when the first stage of labor is not progressing at an expected rate, as the frequency and power of contractions can be directly measured. Contractions that are inadequate in frequency or power may be augmented with an oxytocic agent. Intravenous oxytocin is the drug of choice, as it is effective, inexpensive, and most practitioners are familiar with its usage. Oxytocin has a short half-life, which allows it to be given by continuous infusion and allows for the rapid cessation of its activity when it is discontinued. Labor augmentation with oxytocin can cause uterine hyperstimulation, defined as the presence of six or more contractions in a 10-minute period that causes nonreassuring fetal heart rate abnormalities (such as late decelerations). This would be managed by reduction in dose or discontinuation of the oxytocin, repositioning of the patient, and providing oxygen via face mask to the mother.

Fetal heart tracings (FHT) can be categorized into three categories: I, II, and III, the determination of which further guides management. It is simplest to learn the definitions of categories I and III as category II tends to be everything in between. A category I FHT is considered normal and includes each of the five characteristics: a baseline heart rate of 110 to 160 beats/min, moderate baseline FHR variability, no late or variable decelerations, and both accelerations and early decelerations maybe absent or present. A category III FHT is considered abnormal and includes either absent baseline FHR variability plus any one of the following three: repeated late decelerations, variable decelerations or bradycardia, or a sinusoidal pattern. A category II FHT is considered indeterminable. This category includes a variety of findings, none of which can be categorized into I or III.

During labor, the fetal head descends through the birth canal and undergoes four cardinal movements. During initial descent, the head undergoes flexion, bringing the fetal chin to the chest. As descent progresses, internal rotation occurs, causing the fetal occiput to move anteriorly toward the maternal symphysis pubis. As the head approaches the vulva, it undergoes extension, to allow the head to pass below the symphysis pubis and through the upward-directed vaginal outlet. Further extension leads to the delivery of the head, which then restitutes via external rotation to face either to the maternal right or left side. This corresponds with rotation of the fetal body, aligning one shoulder anteriorly below the symphysis pubis and the other posterior toward the sacrum. Maternal pushing, along with gentle downward traction on the fetal head, will deliver the anterior shoulder, and upward traction similarly delivers the posterior shoulder. Delivery of the remainder of the body will quickly follow. Occasionally, the anterior shoulder will not readily pass below the pubic symphysis. This is called a shoulder dystocia and is an obstetrical emergency, requiring a coordinated effort by the entire medical team to reduce the dystocia. Maneuvers, including hyperflexion of the hips (McRoberts maneuver), suprapubic pressure, cutting an episiotomy, or rotation of the fetal body in the vaginal canal, are attempted and are usually successful.

Of deliveries in the United States, 20% or more are accomplished via cesarean delivery. The most common indications are a history of prior cesarean delivery, arrest of labor or descent, fetal distress necessitating immediate delivery, and breech presentation. Operative vaginal delivery can be performed using either forceps or vacuum assistance. These can only be used when the cervix is completely dilated, membranes are ruptured, the presenting part is the vertex of the scalp, and there is no disproportion between the size of the fetal head and maternal pelvis. If any of these conditions are not met and delivery must be accomplished urgently, a cesarean delivery is indicated.

GBS PROPHYLAXIS

GBS testing is routinely done between 35 and 37 weeks' gestational age. Testing is done by swabbing the vagina, perineum, and anus with a sterile culture applicator.

Current indications for GBS prophylaxis at the time of labor include the following:

• Positive GBS screen collected at 35+ weeks' gestational age

• History of invasive GBS infection in previous infant

• GBS bacteriuria at any time during the current pregnancy

• Unknown GBS status at time of labor plus one of the following:

    • Preterm labor (prior to 37 weeks)

    • Amniotic membrane rupture more than 18 hours

    • Intrapartum fever (temperature >100.4°F)

    • Intrapartum nucleic acid amplification test positive for GBS

Once the need for GBS prophylaxis is determined, an appropriate antibiotic must be given. If no allergy exists, penicillin is the recommended first-line agent. Alternatively, ampicillin could also be used, and this is often institution dependent. If there is no true allergy but intolerance to penicillin, cefazolin should be used. If the patient has a true allergy to penicillin, marked by urticaria, respiratory distress, angioedema, or anaphylaxis, susceptibility of the isolate to erythromycin or clindamycin should be tested. For isolates susceptible to the above alternatives, clindamycin is appropriate; in cases of resistance, vancomycin should be used.

CASE CORRELATION

• See also Case 4 (Prenatal Care).

COMPREHENSION QUESTIONS

16.1 A 21-year-old Gl woman is admitted to the labor unit with spontaneous rupture of membranes. On initial examination, her cervix is 5 cm dilated. Four hours later, her cervix remains unchanged. Which of the following is the most likely diagnosis?

A. Prolonged latent phase

B. Arrest of active phase

C. Arrest of descent

D. Prolonged third stage of labor

16.2 Which of the following is thought to be a result of compression of the fetal head?

A. Early decelerations

B. Variable decelerations

C. Late decelerations

D. Sinusoidal heart rate pattern

16.3 A pregnant woman with an estimated gestational age of 34 weeks presents to the labor triage unit with a clear vaginal discharge. On sterile speculum examination, you see a pool of watery fluid in the vagina. Microscopic examination reveals "ferning:' She states she thinks her"water broke" about 4 hours ago. You determine that this patient is in preterm labor and have to make a decision regarding GBS prophylaxis. Her records indicate that she has had no prior infant with GBS disease and has never tested positive for GBS bacteriuria in current pregnancy. Which of the following is the best step in management of this patient?

A. Since she has no risk factors for GBS, she requires no prophylaxis.

B. She is in preterm labor and would automatically qualify for GBS prophylaxis.

C. A STAT vaginal-rectal GBS swab needs to be done at this time; if positive, GBS prophylaxis would need to be started.

D. Since it has not been more than 18 hours since rupture of membranes, the patient is not at risk for GBS colonization, and therefore nothing needs to be done at this time.

ANSWERS

16.1 B. The cervical dilation beyond 4 cm means active phase. No cervical change for 2 hours is defined as arrest of active phase.

16.2 A. Early decelerations are thought to be caused by fetal head compression. Variable decelerations are caused by cord compression and late decelerations by uteroplacental insufficiency.

16.3 B. One of the indications for GBS prophylaxis is unknown GBS status plus preterm labor. Since this patient is not 35 weeks yet, her GBS status is unknown as routine screening is done between 35 and 37 weeks. Rupture of membranes for less than 18 hours does not preclude her from receiving prophylaxis as she already has the indication of preterm labor that justifies beginning prophylaxis.

CLINICAL PEARLS

⯈ The presence of accelerations on a fetal heart tracing is very reassuring and consistent with a fetal pH of greater than 7.2.

⯈ The use of universal, prenatal screening for GBS and provision of intrapartum antibiotics to women who are colonized can reduce the risk of GBS disease in infants by approximately 50%. Routine screening is recommended at 35 to 37 weeks' gestation.

⯈ Fetal heart rate tracings must be interpreted within the overall clinical situation. Reduction in variability shortly after giving a narcotic pain medication may represent fetal sleep cycle; reduction in variability along with repetitive late decelerations may be an ominous sign of fetal distress.

REFERENCES

Centers for D isease Control and Prevention. 2010 guidelines for the prevention of perinatal group B Streptococcal disease: recommendations and reports. MMWR. 2010;59(RR-10):14-36 

Garite TJ. Intrapartum fetal evaluation. In: Gabbe SG, Niebyl JR, SimpsonJL, eds. Obstetrics: Normal and Problem Pregnancies. 5th ed. New York, NY : Churchill Livingstone; 2007. 

Parer JT, Ikeda T, King TL. The 2008 NICHD standard terminology of fetal heart rate monitoring. Obstet Gynecol. 2009 Jul;114(1):136-138. 

Rouse DJ, St. John E. Normal labor, delivery, newborn care, and puerperium. In: Scott JR, Gibbs RS, Karlan BY, Haney AF, eds. Danforth's Obstetrics and Gynecology. 10th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2008.

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